### Southwest Research Institute ® 

### San Antonio, Texas



# Coastdown and Constant - Speed Testing

Brent Shoffner - SwRI
12/11/2014

# SwRI ®

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# Background

• Current procedure

– US Environmental Protection Agency (EPA) Code of Federal Regulations (CFR) 

# § 1066.310 “Coastdown procedures for vehicles above 14,000 pounds GVWR” .

– This procedure is valid for calculating road load coefficients

 Chassis dynamometer testing

 Aerodynamic input (CD) for the Greenhouse Gas Emissions Model (GEM)

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# Objective

• Investigate modified and new on - road testing methods for evaluating aerodynamic 

# characteristics of Class 7 and 8 tractors.

– Modified EPA Code of Federal Regulations (CFR) § 1066.310 procedure for Class 8 trucks

– Constant speed procedure measuring driveshaft torque and drive wheel torque



# • Evaluate the effect of trailer aerodynamic devices

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# Matrix Variables

• Three trucks evaluated

– 2012 Freightliner Cascadia ®



## – 2012 Kenworth T700

– 2014 International ProStar ®



# • Two truck tire sets

– Primarily a set from a previous SmartWay test program

 “Low rolling resistance”



## – Two tests with as - received truck tire set



# • Same 53’ box trailer in three configurations

– Same “SmartWay” tire set for all tests

 “Low rolling resistance” 5

# 2012 Freightliner Cascadia and 

# 2012 Kenworth T700

• High Roof Sleeper Cabs

6 T700

Cascadia

# 2014 International ProStar

• Donated for use in this program by Environment Canada

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# Two Test Methods

• Modified CFR 40 1066.310 Coastdown

• Constant Speed

– Driveshaft torque



# – Drive wheel torque

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# Coastdown

• Modified CFR 40 1066.310 Coastdown

– Coastdown 70 to zero mph

 Specification – minimum speed at or below 15 

## mph



# – Seven pairs of runs

 The specification is 8 minimum

 Time for each run increased - 15 to zero mph



# – On - board anemometer

– A few tests were conducted with drive wheel torque meters

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# Constant Speed

• Speeds

– 10, 20, 30, 50, 70 mph

– Torque Measurements

 Driveshaft

 Four drive wheels



# – Calculate horsepower

 Based on torque and shaft speeds



# – Calculate road load force

 Truck speed

 Horsepower
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# Additional Instrumentation

• On - board anemometer

• Drive shaft torque meter

• Drive wheel torque meters

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# On - Board Anemometer

• RM Young

– Model 81000



### – Trailer mounted

 A = .85 m

 B = .97 m



### – Constant speed calibration

 Truck speed

 Wind speed

12 Top of Trailer

# Driveshaft Torque Meter

13 

## • Drive shaft torque meter

 Modify drive shaft and 

### mount antenna

 HBM Model T40B
o - 5K to +5K Nm o Shaft speed calculated o ERPM and trans gear &/or o Axle ratio & wheel speed

Antenna

# Constant Speed Tests

• Drive wheel torque meters

– Michigan Scientific 

### Corporation

 Mounted between the hub & the wheels as shown

 Torque range
o - 2000 to +2000 lb - ft o Over - range protection


###  Accuracy
o 0.1% full scale



### – Wheel speed (RPM)



###  Truck speed from the optical 5 th 

### wheel
o R 2 =1.000 correlation
14 Strain gauges

# Trailer Information

• “Standard trailer” for high roof tractors

– CFR 40 CFR § 1037.501

– No Ballast

– Cab to trailer gap – 45 - 47”

 No gap reducer

• Same tire set for all tests

• “Low rolling resistance”

• Used in a previous EPA SmartWay test program

• Size 295 / 75 / 22.5

• 100 PSI

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# Standard trailer plus two aero 

# configurations tested

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# Designation Description Configuration 1 Standard Trailer
– no enhanced

aero 

# Configuration 2 Trailer skirt Configuration 3 Trailer skirt and tail aero

# 53’ Box Trailer Configurations

17 Configuration 1 Configuration 2

Configuration 3

# Test Road

• Texas Farm to Market Road 70

– East - West section between Chapman Ranch and 

### Bishop

– Meets 40 CFR 1066.310 specifications

– Survey data used to calculate the effect of slight grade changes on road load force

18 Google Maps Seven pair of runs

# Road Load Force

• Force to maintain a given constant speed

– Level road

– Standard air temperature and pressure



# – No Wind

19 Tractive Road Load Force
Road Load Force

# Typical Road Load Force Curve

Aerodynamic drag Drag Area (C D A) (m 2 ) = 2xD adj / ρ ρ =air density at reference conditions = 1.17 kg/m 3

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### Mechanical Road Load Force = D adjusted x(Truck Speed) 2 +A mech adjusted

# Coastdown

• Additional Considerations

– Rotational inertia of 18 wheel and tire assemblies

 6% of the total truck mass

– Rotational resistance of the axles and transmission

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# Constant Speed

• Additional Considerations

– Driveshaft torque includes energy losses in the axles under load

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# Results – Test Truck 1

23 Configuration # 1 No Aero # 2 Trailer Skirt # 3 Trailer Skirt & Tail Aero Method Coastdown Driveshaft Torque Coastdown Driveshaft Torque Coastdown CDA (m^2) 6.91 6.62 6.37 5.93 5.60 Delta vs Conf 1

- - 0.54

- 0.69

- 1.31

# Truck 1 Coastdown Results

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# Results – Test Truck 2

25 Configuration # 1 No Aero # 2 Trailer Skirt # 3 Trailer Skirt & Tail Aero Method Coastdown Driveshaft Torque Wheel

Torque Coastdown Coastdown

Rerun Driveshaft

Torque Coastdown CDA (m^2) 6.66 6.23 5.90 6.26 6.20 6.02 5.73 Delta versus Conf 1

- - - - 0.40

- 0.46

- 0.21
- 0.93

# Truck 2 Coastdown Results

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# Truck 3

27 Config

uration # 1 No Aero # 2 Trailer Skirt # 3 Trailer Skirt & Tail Method Coast

down * Coast

down Drive shaft Torque Wheel Torque Coast

down * Coast

down Drive shaft Torque Wheel Torque Coast

down Drive shaft Torque Wheel Torque CDA (m^2) 6.41 6.21 6.16 5.97 5.69 5.76 5.78 5.55 5.36 5.17 4.96 Delta vs. Conf 1

- - - - - 0.72

- 0.45

- 0.38

- 0.42

- .85

- 0.99

- 1.01 * As

- received truck tires

# Truck 3 Coastdown

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# Truck 3 – Constant Speed – Driveshaft Torque

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# Truck 3 – Constant Speed – Wheel Torque

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# Truck 3 – Configuration 1 (no trailer aero)

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# Truck 3 – Configuration 2 (trailer skirt)

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# Truck 3 – Configuration 3

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# Summary / Learning

• The constant speed test method is potentially a viable approach for determining road load coefficients

• In this program both the coastdown and the constant speed test methods did discriminate between the three 

## trailer aero configurations in terms of the drag area / D adjusted 

## term

• The delta in the drag area was similar between the three trailer configurations with all three trucks

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# Southwest Research Institute ®

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